Body tissues subject to proliferative tissue disorders, such as malignant tumors, are often treated by surgical resection of the tumor to remove as much of the tumor as possible. Unfortunately, the infiltration of the tumor cells into normal tissues surrounding the tumor may limit the therapeutic value of surgical resection because the infiltration can be difficult or impossible to treat surgically. Radiation therapy may be used to supplement surgical resection by targeting the residual tumor margin after resection, with the goal of reducing its size or stabilizing it. Radiation therapy may be administered through one of several methods, or a combination of methods, such as interstitial or intercavity brachytherapy. Brachytherapy may also be administered via electronic brachytherapy using electronic sources, such as x-ray sources, for example.
Brachytherapy is radiation therapy in which the source of radiation is placed in or close to the area to be treated, such as within a cavity or void left after surgical resection of a tumor. Brachytherapy may be administered by implanting or delivering a spatially confined radioactive material to a treatment site, which may be a cavity left after surgical resection of a tumor. For example, brachytherapy may be performed by using an implantable device (e.g., catheter or applicator) to implant or deliver radiation sources directly into the tissue(s) or cavity to be treated. During brachytherapy treatment, a catheter may be inserted into the body at or near the treatment site and subsequently a radiation source may be inserted through the catheter and placed at the treatment site.
Brachytherapy is typically most appropriate where: 1) malignant tumor regrowth occurs locally, within 2 or 3 cm of the original boundary of the primary tumor site; 2) radiation therapy is a proven treatment for controlling the growth of the malignant tumor; and 3) there is a radiation dose-response relationship for the malignant tumor, but the dose that can be given safely with conventional external beam radiotherapy is limited by the tolerance of normal tissue. Interstitial and/or intercavity brachytherapy may be useful for treating malignant brain and breast tumors, among other types of proliferative tissue disorders.
There are two basic types of brachytherapy, high dose rate and low dose rate. These types of brachytherapy generally include the implantation of radioactive “seeds,” such as palladium or iodine, into the tumor, organ tissues, or cavity to be treated. Low dose rate (LDR) brachytherapy refers to placement of multiple sources (similar to seeds) in applicators or catheters, which are themselves implanted in a patient's body. These sources are left in place continuously over a treatment period of several days, after which both the sources and applicators are removed. High dose rate brachytherapy (HDR) uses catheters or applicators similar to those used for LDR. Typically, only a single radiation source is used, but of very high strength. This single source is remotely positioned within the applicators at one or more positions, for treatment times which are measured in seconds to minutes. The treatment is divided into multiple sessions (‘fractions’), which are repeated over a course of a few days. In particular, an applicator (also referred to as an applicator catheter or treatment catheter) is inserted at the treatment site so that the distal region is located at the treatment site while the proximal end of the applicator protrudes outside the body. The proximal end is connected to a transfer tube, which in turn is connected to an afterloader to create a closed transfer pathway for the radiation source to traverse. Once the closed pathway is complete, the afterloader directs its radioactive source (which is attached to the end of a wire controlled by the afterloader) through the transfer tube into the treatment applicator for a set amount of time. When the treatment is completed, the radiation source is retracted back into the afterloader, and the transfer tube is disconnected from the applicator.
A typical applicator catheter comprises a tubular member having a distal portion which is adapted to be inserted into the patient's body, and a proximal portion which extends outside of the patient. A balloon is provided on the distal portion of the tubular member which, when placed at the treatment site and inflated, causes the surrounding tissue to substantially conform to the surface of the balloon. In use, the applicator catheter is inserted into the patient's body, for instance, at the location of a surgical resection to remove a tumor. The distal portion of the tubular member and the balloon are placed at, or near, the treatment site, e.g. the resected space. The balloon is inflated, and a radiation source is placed through the tubular member to the location within the balloon.
Several brachytherapy devices are described in U.S. Provisional Patent Application 60/870,690, entitled “Brachytherapy Device and Method,” and U.S. Provisional Patent Application 60/870,670, entitled “Asymmetric Radiation Dosing Devices and Methods,” both filed on Dec. 19, 2006, which are both commonly owned with the present application, and with copending U.S. patent application entitled “Asymmetric Radiation Dosing Devices and Methods,” filed on or about Dec. 18, 2007, U.S. Pat. Nos. 5,913,813, and 6,482,142, all of which are hereby incorporated by reference herein in their entireties.
The dose rate at a target point exterior to a radiation source is inversely proportional to the square of the distance between the radiation source and the target point. Thus, previously described applicators, such as those described in U.S. Pat. No. 6,482,142, issued on Nov. 19, 2002, to Winkler et al., are symmetrically disposed about the axis of the tubular member so that they position the tissue surrounding the balloon at a uniform or symmetric distance from the axis of the tubular member. In this way, the radiation dose profile from a radiation source placed within the tubular member at the location of the balloon is symmetrically shaped relative to the balloon. In general, the amount of radiation desired by a treating physician is a certain minimum amount that is delivered to a region up to about two centimeters away from the wall of the excised tumor, i.e. the target treatment region. It is desirable to keep the radiation that is delivered to the tissue in this target tissue within a narrow absorbed dose range to prevent over-exposure to tissue at or near the balloon wall, while still delivering the minimum prescribed dose at the maximum prescribed distance from the balloon wall (i.e. the two centimeter thickness surrounding the wall of the excised tumor).
However, in some situations, such as a treatment site located near sensitive tissue like a patient's skin, the symmetric dosing profile may provide too much radiation to the sensitive tissue such that the tissue suffers damage or even necrosis. In such situations, the dosing profile may cause unnecessary radiation exposure to healthy tissue or it may damage sensitive tissue, or it may not even be possible to perform a conventional brachytherapy procedure.
To alleviate some of these problems associated with prior applicators, an asymmetric dosing profile is produced by shaping or locating the radiation source so as to be asymmetrically placed with respect to the longitudinal axis of the balloon. In an alternative approach, the applicator is provided with asymmetric radiation shielding located between the radiation source and the target tissue.
However, asymmetrically placing the radiation source decreases the radiation dosing profile in certain directions, but correspondingly increases the radiation dosing profile in the other directions. Some devices may not allow for adjustment of the amount of asymmetry and/or the resulting radiation dosing profile shape. Accordingly, there remains a need for additional methods and devices which can provide an asymmetric radiation dosing profile having a predetermined orientation during brachytherapy procedures.